The present invention relates to methods of making compositions comprising a water-responsive polymer and clay particles. Particularly, the present invention relates to methods of making compositions comprising melt blending organically modified clay or layered silicate particles and a water-responsive polymer that is optionally degradable, desirably environmentally degradable. In an exemplary embodiment, the water-responsive polymer is a polymer of ethylene oxide. In another embodiment, the water-responsive polymer is a graft copolymer of ethylene oxide.
Disposable personal care products such as pantiliners, diapers, tampons, etc. are a great convenience. Disposable products provide the benefit of one time, sanitary use and are convenient, quick and easy to use. However, disposal of products is a concern. Incineration of products is not desirable because of increasing concerns about air quality and the costs and difficulty associated with separating incineratable products from non-incineratable articles. Dumping of products is also undesirable due to concerns with limited landfill space and increasing land cost. Consequently, there is a need for disposable products which may be quickly and conveniently disposed of without dumping or incineration.
It has been proposed to dispose of these products in municipal and private sewage systems. Ideally, these products would be both flushable and degradable, desirably biodegradable, in conventional sewage systems. Articles suited for disposal in sewage systems that can be flushed down conventional toilets are termed xe2x80x9cflushable.xe2x80x9d Disposal by flushing provides the benefit of providing a simple, convenient and sanitary means of disposal.
Flushable products must have sufficient strength under the conditions in which they will be used. Thus, it is desirable for flushable personal care products to withstand the elevated temperature and humidity conditions encountered during use, yet lose integrity upon contact with water in the toilet. It is also desirable that these personal care products are breathable in order avoid the build-up of perspiration and increase the level of comfort of the consumers of these products. Therefore, a breathable material having mechanical integrity when dry and that readily disintegrates upon immersion in water is highly desirable.
Due to its unique interaction with water and body fluids, poly(ethylene oxide) (hereinafter PEO) is currently being considered as a component material for water-sensitive compositions. PEO,
xe2x80x94(CH2CH2O)nxe2x80x94
is a commercially available, water-soluble polymer that can be produced from the ring opening polymerization of the ethylene oxide, 
Because of its water-solubility and breathability, PEO is desirable for flushable and personal care applications. Although conventional PEO films are not as fluid stable as desired for many personal care applications and are difficult to process using conventional processing techniques, modified PEO compositions are being developed that are amenable to conventional melt processing. There is still a need to further improve the liquid stability of water-responsive an degradable polymer compositions.
Many have attempted to overcome these difficulties. U.S. Pat. No. 4,902,553 to Hwang et al. describes disposable articles comprising a liquid impermeable, vapor permeable film. The liquid impermeable, vapor permeable film described by Hwang et al. comprises a crystallizable, stretched polyolefin-based film and a rattle-reducing additive which may be poly(ethylene oxide). However, the liquid impermeable, vapor permeable films of U.S. Pat. No. 4,902,553 require at least one nucleating agent which may be talc or calcium carbonate and stretching to achieve breathability. The amounts of nucleating agent are limited to very small amounts, 0.05 to 5 percent by weight. These amounts of inorganic, nucleating agent are insufficient to be defined as fillers. Further, stretching is required to generate porosity and hence breathability and subsequent leaching of the rattle-reducing agent is desired. In contrast, the films of the present invention do not require stretching for breathability and do not necessarily require a nucleating agent or a crystallizable polyolefin. Normally, the addition of inorganic filler to a polymer without stretching to create voids does not enhance the breathability of the polymer. Conventional fillers such as mica, calcium carbonate and kaolin are not expandable. Many of these conventional fillers are plate-like in shape and provide barriers to the diffusion of air and vapors.
U.S. Pat. No. 3,895,155 describes coated, transparent plastic articles. The transparent plastic may comprise poly(ethylene oxide). An inorganic, protective coating is applied as a separate layer over the transparent plastic article to improve surface hardness, increase stretch resistance, and facilitate non-fogging. The inorganic, protective coating may comprise various metal oxides. However, the coating forms a separate, discrete, glass-like layer from the transparent plastic article and the resulting coating and articles are not breathable or flushable.
U.S. Pat. Nos. 5,075,153, 5,244,714, and 5,672,424 to Malhotra et al. describe multilayered or coated recording sheets designed for electrostatic printing processes. The recording sheets comprise a base sheet with an anti-static layer, which may be made from poly(ethylene oxide). The recording sheets comprise an additional toner-receiving layer, which comprises inorganic oxides such as silicon dioxide, titanium dioxide, calcium carbonate, or the like. The poly(ethylene oxide) and inorganic oxides are contained in separate layers, the anti-static layer and the toner-receiving layer respectively. The recording sheets are not breathable or flushable.
U.S. Pat. No. 4,276,339 to Stoveken describes a laminated product comprising a paper layer and a foamed layer. Poly(ethylene oxide) is described as one of many possible components of an aqueous dispersion of latexes from which the foamed layer is made. Inorganic fillers such as clay or silica are suggested as possible additions to the aqueous dispersion of latexes in order to increase the solids content and density of the aqueous dispersion of latexes. The aqueous dispersion from which the foamed layer is made must be capable of being foamed and requires foaming in order to be breathable.
Currently available water-responsive, degradable and breathable compositions are not as stable when in contact with aqueous fluids as desired for many personal care applications. What is needed in the art is a means to improve the stability of water-responsive resins in contact with aqueous fluids. What is also need in the art is a method for making and controlling the fluid stability and degradability of water-responsive resins when in contact with aqueous fluids and for improving the processability of water-responsive, degradable and breathable compositions.
The present invention provides a method of producing compositions with controlled mechanical and/or structural stability when in contact with aqueous fluids. The compositions of the present invention comprise a blend of at least two components: (1) a polymer that is water-responsive and optionally degradable and (2) organically modified clay particles and/or organically modified layered silicate particles. Suitable water-responsive polymers include polymers and copolymers of ethylene oxide and other polar polymers whose properties degrade when exposed to water and aqueous solutions. Suggested water-responsive polymers include polar polymers with ester groups including degradable polyesters and polylactides. Desirably, the water-responsive polymer is environmentally degradable, particularly biologically degradable. Suitable organically modified clays include organically modified clays from the smectite group, such as montmorillonites and bentonites. Compositions, films, fibers and articles made by the method of the present invention have controlled degradability and enhanced stability when in contact with aqueous liquids, fluids and droplets. In addition, the compositions of the present invention provide enhanced mechanical stability when exposed to aqueous fluids, including liquids and vapors. These improvements make the compositions of the present invention more suitable for applications on flushable films, fibers and articles. An unexpected benefit of the addition of organically modified clay to PEO is improved melt processability of the PEO.
Surprisingly, the addition of organically modified clay or layered silicate particles to poly(ethylene oxide) improves the melt processability of the poly(ethylene oxide). Normally, unmodified poly(ethylene oxide) resins are not extrudable, especially at high and ultra high molecular weights, including up to 8,000,000 gram/mol viscosity average molecular weight. Dramatic improvements in the melt processability of poly(ethylene oxide) are observed with the addition of organically modified clay particles to poly(ethylene oxide) resins having average molecular weights of 1,000,000 grams per mole to 8,000,000 grams per mole.
Compositions, films and fibers made of the present invention are especially useful for manufacturing personal care articles with potential flushable and environmentally degradable or compostable applications, such as, diapers, feminine pads, pantiliners, training pants, and other articles incorporating flushable and environmentally degradable compositions and components. Other suggested uses for compositions, films and fibers of the present invention include the manufacture of health care articles, such as, bandages, gowns and wound dressings.
Key variables that effect the fluid stability of the compositions of the present invention include, but are not limited to: filler type, filler particle size and size distribution, filler expansion and swelling efficiency, filler interaction with the polymer and associated water, and molecular weight and selection of the water-responsive polymer component(s). In one embodiment of the present invention, the filler particles desirably have an average particle size which is not more than about 50 microns. More desirably, the filler particles have an average particle size that is not more than about 10 microns. Even more desirably, the filler particles have an average particle size that is not more than about 5 microns. Reduced particle sizes provide improved dispersion and processability.